<!DOCTYPE html>
<html>
<head>
	<title></title>
</head>
<body>
	<canvas id="canvas" width="500" height="500" style="border:1px solid #000"></canvas>

</body>
</html>

<script type="text/javascript">
	var canvas = document.getElementById('canvas');
	var context = canvas.getContext('2d');
	context.arc(200,200,100,0,Math.PI*2,true);
	context.stroke();
	context.beginPath();
	context.strokeStyle ="#ff0000";
	context.lineWidth=3;
	context.arc(200,200,100,Math.PI/3,Math.PI*4/3);
	context.stroke();
	context.closePath();

</script>